Solar panels. Solar water heating systems = Solar panels + solar energy. Solar thermal: solar power & solar hot water. Solartwin review LCA / CoP.
Coefficient of performance in renewables – A hidden secret.
In any context, but in particular that of the Renewable Heat Incentive (RHI), the coefficient of performance (CoP) is a generic concept across all renewables and it is, to some extent, similar to the financial concept of rate of return on investment, or of interest on a loan. It is just as important too.
The importance of CoP is a hidden information timebomb.
- It seems that much (but not all) of Europe’s self-regulating renewables industry do not want the consumer to know too much about CoP. It worthy of note that attempts to have such figures published widely across the sector have not been agreed by UK’s main gateway for grants, the Microgeneration Certification Scheme. Any pretentions that such industry-led “quality” schemes may have to be champions of consumer choice are questionable on such crucial issues of transparency. Publication of CoP is also being actively delayed or blocked, for certain technologies, even at a European Standards (CEN) level.
“Parasitics” are a general energy industry blind spot and not just a problem with renewables.
- The UK the gas and oil boiler industry are omitting to report the mains electric parasitics of their technologies. Here’s a case study. Let’s say that you have a brand new boiler-scrappage grant aided condensing boiler for which the supplier claims a “SEDBUK efficiency” of 95%. Does this 95% figure account for the fact that this boiler’s internal minicomputer uses mains electricity 24 hours a day, even when it is not operating? No. So its total energy efficiency will actually be lower than 95%. And that it uses more electricity on top of this as soon as it lights up, and its internal electric valves, fans and pumps start running? Of course not. So, the figure will be lower still. It appears that market-grabbing top-end SEDBUK efficiency figures have actually been delivered by boiler makers at the expense of sustainability. All operational (but not manufacture) energy consumption needs to be included in a CoP calculation. Not excluded, as in SEDBUK.
The green consumer bodies have more work to do.
- Why have Friends of the Earth, the Energy Saving Trust, the Carbon Trust and other supposed independent think tanks so abjectly failed to deliver something more useful to the public that mere SEDBUK efficiency figures? Why should the consumer put up with being told half of the story? Telling someone to install a more efficient gas boiler surely needs to be coupled with accurate information on what negative effect this “upgrade” might have on their electricity bill.
But returning to CoP. In summary, which CoP is best?
- The higher the CoP the better. For water heating, a CoP of 1:1 is pointless: you might as well just use an immersion heater. Ideally, an infinite CoP is desirable. An infinite CoP is what sunny south facing windows will give you, provided that you can use the solar heat energy which arrives via them. An infinite CoP is also available from PV (solar electric) pumped solar water heating systems.
Moving into CoP in microgeneration.
- If someone says to you that their domestic heat pump has an average annual energy coefficient of performance of 3 : 1, this means that it delivers three times more heat energy than it uses in its motors and compressors and associated electronics. So for every kilowatt-hour (“unit”) of electricity which it burns up and which you pay for, it delivers three times that amount of heat to your home. Great – provided this is sustainable. Of course CoP applies just as well to wind turbines, photovoltaics, and water turbines, all of which burn up use electricity 24/7 to run their electrical controls, displays, power conditioning units and inverters, even when there is no wind sun or water about to run them.
The very same CoP concept applies to solar water heating.
- A leading mains pumped evacuated tube solar water heating system has a CoP 1:13. according to independent studies. Try googling “side by side testing of eight solar water heating systems”. Appendix C9 of this report, for example, shows that a leading evacuated tube system consumed 82-92 kWh of bought in energy for every 1000 kWh of energy it delivered. This gives it an average CoP if 11.4 in terms of energy.
What is interesting is that CoP can also be described in terms of carbon, as well as in terms of energy. (It can also be done financially, of course.)
- How much carbon do you have use to save a tonne of carbon? is the question here. The answer depends on the relative “carbon intensity” of the electricity used for pumping, compared with that of the sometimes different fuel which is saved by having solar water heating. Given that mains gas is the commonest water heating fuel in UK, we shall look at its relative carbon intensity here. In the side by side report referred to earlier, it is stated that the carbon intensity of gas is 2.5 times less than that of electricity.
Operational or whole of life perspectives?
- So the 11.4 energy CoP of these solar tubes translates into a carbon CoP of 1:4.6. Not so good, but still positive. But this only looks at the operational side. What if the technology uses energy to make it? Of course all do, so you start with a negative balance sheet here. So, as a consequence there are breakeven times to be asked about. At this stage we have only been looking at operational CoP. The actual energy or carbon impacts due to their manufacture or installation have not been included. To do so involves widening the scope once again to look at life cycle analysis of microgeneration technologies. Bath University have studied matter this extensively. They report that 15% of the total lifetime energy delivery of a solar electric system is accounted for (ie negated) by its energy of manufacture and disposal and that for a solar water heating system the figure is three times better, at only 5%. Here is a summary of some of the Bath University research on life cycle analysis of micro-renewable energy systems.
Infinite CoP is available for some microrenewables.
- Are there solar water heating systems which may have an infinite CoP in terms of energy or carbon? Interestingly, the answer is yes. You just need to get rid of the mains electricity supply. Thermosyphon (gravity pumped) and solar electric (PV / photovoltaic) pumped solar (such as Solartwin) can have a zero operational energy requirements. So their CoP is infinite and they have no “carbon clawback”. This approach obviously pleases green consumers. It is interesting that grants schemes do not seek to reward the delivery of high CoP in solar. Perhaps solar thermal should have a grant eligibility threshold for state aid of say 1: 20 or better? Adopting this approach would green up the solar industry pretty quick!
No wonder the solar industry wants to keep this debate closed down!
- Solar Twin Ltd once dared to publish the names of the solar technologies whose energy and carbon clawbacks were reported in the side by side test report. We were promptly prevented from publishing them so by certain influential thugs in the solar industry. We censored the names and we published only averages, not brand-by brand data as we had hoped to do.
- “Over the life of my proposed new renewable energy technology, if you load all its life cycle and operational energy and carbon costs up-front over, say, a 25 year lifespan, how long will it take to pay back?” is a question which some big players in the European energy technology industry are rather reluctant to answer.
If you are member of a consumer organisation such as Which?, please, please ask them to press for such data to be made public. The industry will be unlikely to volunteer it in a hurry.